Many vehicles are equipped with safety devices such as airbags and seat belts to protect persons occupying seats in the vehicle. The manner in which an air bag engages the vehicle occupant during an accident may be influenced by factors such as the force with which the occupant moves against the air bag and the inflation pressure of the air bag. Examples of conditions that may effect occupant momentum and inflation pressure include vehicle dynamics (such as deceleration), and vehicle occupant characteristics such as the weight and position of the occupant.
It is known to adjust a restraint system to accommodate for the weight and position of a vehicle occupant. For example, if a seat is unoccupied, it may not be necessary to activate an air bag or other safety device associated with that seat. In addition, if a seat is occupied by a person of a particular size the deployment of a safety device may be varied accordingly. For example, a relatively large vehicle occupant may require a fully pressurized air bag during a collision, whereas a smaller occupant, such as a child, may require only a fraction of available air bag inflation pressure. In the case of an infant seated in a safety seat or car seat, it is desirable to prevent any air bag deployment due to known risks of infant injury.
One type of sensor used to sense the weight of a vehicle occupant is a resistive strain gauge sensor. With such a sensor, force or pressure is sensed based on the strain placed on resistors. Other exemplary mechanisms of sensing weight include locating multiple pressure transducers in a layer of polymer within the seat cushion, an array of flat, mat-like contact switches having contact surfaces separated by a deformable layer and within the seat cushion, and an array of piezoelectric or thin-film sensors mounted to the bottom of the vehicle seat.